Device for cleaning of screens in cellulose digesters

ABSTRACT

Screens inserted in the shell of a continuous cellulose digester are cleaned by a liquid under high pressure pumped through a sector of the screen during the normal operation of the digester and while the rest of the sd for drawing off digesting liquor from the fibrous material in the digester. The cleaning liquid passes the screen in the opposite direction to the digesting liquor and works loose fibers wedged into the slits of the screen. On the pulp side of the screen the sector being cleaned is blinded off by a turning cover plate, and the space back of screen is divided into sector-shaped compartments. By means of valves a conduit for circulating cleaning liquid is connected to the space within the sealing edge of the cover plate and to the opposite compartment. By turning the cover plate and adjusting the valves one screen sector at a time as well as the corresponding compartment and connected conduits are cleaned and fibers and deposits removed therefrom.

United States Patent Johan c. F. c. Richter [72] Inventor St. Jean CapFerrat, France (21] Appl, No. 759,632 [22] Filed Sept. i3, [968 [45]Patented June 29, 1971 [73] Assignee AktiebolagetKamyr Karlstad, Sweden[32] Priority Sept. 15, 1967 [33] France 12,729/67 [54] DEVICE FORCLEANING 0F SCREENS IN CELLULOSE DIGESTERS 4 Claims, 4 Drawing Figs.

[52] U.S..Cl 210/411, 162/251,162/275,209/380,210/415 [51] Int. Cl B07b1/50 [50] Field of Search... [62/272,25l.48.60.274.275;210/4l5.411.4|2,395:209/380 [56] References CitedUNITED STATES PATENTS 3,434,920 3/1969 Green 162/251 X 3,360,907 1/1968Clark et a1. 210/411 X FOREIGN PATENTS 146,907 7/1954 Sweden PrimaryExaminerS. Leon Bashore Assistant Examiner-R. H. Tushin Att0rneyCushman,Darby and Cushman ABSTRACT: Screens inserted in the shell ofa continuouscellulose digester are cleaned by a liquid under high pressure pumpedthrough a sector of the screen during the normal operation of thedigester and while the rest of the sd for drawing off digesting liquorfrom the fibrous material in the digester. The cleaning liquid passesthe screen in the opposite direction to the digesting liquor and worksloose fibers wedged into the slits of the screen. On the pulp side ofthe screen the sector being cleaned is blinded off by a turning coverplate, and the space back of screen is divided into sector-shapedcompartments. By means of valves a conduit for circulating cleaningliquid is connected to the space within the sealing edge of the coverplate and to the opposite compartment. By

'tuming the cover plate and adjusting the valves one screen PATENTEUJUN29|971 SHEET 2 OF 2 INVENTOR uunw crc 5cm.-

ATTORNEYS DEVICE FOR CLEANING F SCREENS IN CELLIUILOSEllItllGlES'lIlElRS The invention relates to a device for cleaning ofscreens inserted in containers for treatments, particularly digestion,of finely comminuted cellulosic material, and serving for straining offliquid from the cellulosic material. Particularly the invention relatesto a screen-cleaning device of the kind comprising a movable cover platearranged on the fiber material side of the screen, which cover plate hasan edge surrounding and sealing off a portion of the face of saidscreen, a conduit for cleaning liquid being connected to the spacebetween said screen part and said cover plate.

In a known device of said kind, as described in Swedish Pat. No. 146,907liquid taken from the space behind the screen is forced back through thescreen and is carried off together with particles worked loose from thescreen apertures through the conduit connected to the cover plate. Thus,the screen is cleaned by a flow of liquid of the kind mixed with thecellu losic material, and also the possible fluid pressure isrestricted.

The object of the present invention is to improve screencleaning devicesof the above-mentioned kind so as to make them more efficient. A chamberback of the screen is divided up into compartments separated from eachother and connected to individual conduits. Thereby the cleaning liquidflow can be made independent of the function of the screen and can takeplate without disturbing the same. For instance, cleaning liquid may beforced through the screen with a considerably higher pressure than thepressure of the container, so that the force exerted by the cleaningliquid upon the particles clogging the screen apertures can be madegreater than the force by which they have been wedged into the sameduring the previous screening period, and consequently said particlescan be worked loose more easily. Furthermore, the cleaning liquid can beheld separated from the liquid mixed with the cellulosic material,involving the possibility of using any suitable kind of cleaning liquid,e.g. a chemically active liquid, which dissolves heavily adheringdeposits upon the screen and which is of such a kind that it should notbe mixed into the liquid treating the cellulosic material. For instance,in screens used for drawing off dissolved reaction products from thefibrous material after a prehydrolysis step in a continuous cellulosedigester, clogging deposits will often form in the screen aperturesalready after a few hours of operation and obviously it is a greatadvantage to be able to perform during the continuous operation of thedigester, a dissolution of the deposits by means of a scavenging flow ofsodium lye or similar caustic chemicals.

An embodiment of the device according to the invention will be moreclosely described herein below with reference to the accompanyingdrawings, in which FIG. 1 is a vertical sectional view of the screenaccording to the invention, FIG. 2 is a horizontal sectional view of thescreen, FIG. 3 is an elevational view thereof taken from the right-handside in FIG. l, and FIG. 4 is a vertical sectional view taken from theline lV-IV of FIG. ll.

Referring to FIGS. l and 2, the number 11 designates the cylindricalshell of an upright cylindrical cellulose digester adapted for carryingout continuous digester of cellulosic material, such as wood chips. Atthe level of the digester where the wood chips should be relieved ofused liquor and reaction products, such as black liquor with anadmixture of prehydrolysate, there are inserted in the digester shell anumber of screens, only one thereof being shown in the drawings.

The shown screen is composed of a number of parallel, closely setvertical screen rods 13 and a screen chamber 15 back thereof. The latteris formed by a back wall 17 and a cylindrical flange 19 having a recessagainst which the screen rods rest with their ends and are held evenlyspaced so that their sides facing the interior of the digester form aflat circular surface in which there are parallel slits of a suitablewidth for retaining the chips and letting the digesting liquor through.These screening rods and the chamber form a unit which is inserted in anannular flange 21 integral with the digester shell and is attachedthereto by means of a flat annular flange 23 in such a position thatsaid flat screen surface is flush with the digester wall 11 or somewhatretracted.

Approximately half of the screen surface at a time is covered by ahalf-circular cover plate 25 or eyelid" attached to a hollow shaft 27extending centrally through the screen and its chamber. Said shaft isjournaled in a central bearing sleeve 29 integral with the backwall 17of the screen chamber and extending therefrom in the forward as well asin the backward direction. The shaft 27 is sealed to said bearing sleeveby means of a stuffing box 31. Attached to the backward end of the shaftis a handle 33 or other operating means whereby the shaft and the coverplate 25 attached thereto can be turned and set in any desired angularposition. Normal positions are the position shown and the diametricallyopposite position obtained by a turning movement of In both of saidpositions the straight edge 35 of the cover plate is vertical andparallel to the screen rods 13, so that the cover plate offers the leastpossible resistance to movement of the chips in the length direction ofthe digester and so that the exposed slits between the screen rods areswept in their entire lengths by the chips, a certain automatic cleaningeffect being obtained.

The cover plate 25 is somewhat convex or domed inwardly but its straightedge 35 as well as its half-circular edge 37 fit closely to the screenso that a cavity 9 closed off from the digester is formed on the backside of the cover plate. Via the central bore 411 and radial bores 43 inthe shaft 27 said cavity communicates with a space 45 in the bearingsleeve 29, which space is connected by means of a conduit 47 to amanifold 49 common to several screens. Such liquid as enters the cavity39 from the screen chamber is let out in the described path.

By means of a diametrically extending vertical partition 51 (FIG. 4) thescreen chamber 15 is divided upon into two compartments 53, 55,completely separated from each other. In each of the several screenunits the left-hand compartment 53 communicates via a conduit 57extending through the backwall 17, with a manifold 59, whereas theright-hand compartment of each screen communicates over a conduit 61with a manifold 63. By means of a three-way valve 65 the manifold 59 canbe connected either to a main discharge conduit 67 for extracteddigesting liquor and/or to a scavenging liquid conduit 69. Similarly themanifold 63 can be connected by means of a three-way valve 71 either tothe conduit 67 or the conduit 69. The two three-way valves should alwaysconnect the manifolds differently, and therefore they are preferablymechanically coupled so as to be reset simultaneously and in a fixedrelation.

The conduit 69 is connected to the manifold 49 over a motor'driven pump73, so that said pump can maintain a circulation of liquid which whenthe cover plate 25 takes the position shown runs in the loop 73, 69, 65,59, 57, 53, 39, 41, 43, 45, 47, 49, 73. Cleaning liquid which may bestrong sodium lye, is introduced into said loop from a supply tank 75.When the cleaning liquid has become too contaminated with dissolvedimpurities, it is drained through conduit 79 by opening valve 77. Duringsaid cleaning of one screen half the other can be used for withdrawingdigesting liquor which is discharged through 55, 61, 63, 71, 67. After awhile a shift is made by turning the cover plate 25 through 180 andresetting the three-way valves. The cleaning liquid passes from the pump73 through 69, 71, 63, 61, 55, 39, 41, 43, 45, 47, 49 back to the pump,and simultaneously the withdrawn digesting liquor runs through 53, 57,59, 65 to the draining conduit 67.

It is apparent apparent that the cleaning liquid will clean not only thescreen proper but also all parts of the screen chamber back thereof andalso the manifolds 49, 59, 63 as well as all conduits connected theretoand the three-way valves.

The shown embodiment is merely an example which may be modified invarious respects within the scope of the invention as set forth in thefollowing claims. Thus, in principle, it is possible to have the coverplate blind merely a small sector of the screen; then the screen chambermust be divided up into a greater number of chambers having acorrespondingly smaller angular extension. Thus, if the cover plateforms a sector of 120, the screen chamber must be divided in threecompartments by means of radial partitions.

On account of the independent scavenging system it is possible to usefor the cleaning another liquid than the liquid mixed with theeellulosic material for treating the same, but obviously said latterliquid may also be used for the cleaning purpose here contemplated. Inthis case the invention offers the advantage that the cleaning can takeplace at a higher pressure than the pressure prevailing in the digester,because the cover plate seals off the pressure of the cleaning liquid.ln screens inserted in a container for treatment of pulp at a lowtemperature, the invention offers the possibility of cleaning thescreens with heated liquid of one kind or another.

What I claim is:

1. Apparatus for cleaning of screens inserted in containers fortreatment of finely comminuted eellulosic material and serving fordrawing off liquid from the eellulosic material, said apparatuscomprising: a cover plate covering a portion of the screen; means formoving the cover plate over the screen on the eellulosic material sidethereof, said cover plate having an edge closely applied against thescreen and surrounding a part of its surface and defining a cavity withsaid surface; a cleaning liquid discharge conduit extending through thecover plate and opening out into said cavity; means defining a chamberlocated on the opposite side of the screen from the cover plate;partition means dividing said chamber into separate compartments, saidpartition means having edges adjacent said screen opposite said coverplate which cooperate with the edge of said cover plate to maintain saidcavity in communication with a given compartment, and a separate conduitconnected to each compartment for delivery thereto a stream of cleaningliquid when said cavity is in communication with said given compartmentwhereby cleaning liquid will flow through said screen from said givencompartment to said cavity and out through said discharge conduit.

2. Apparatus as in claim 1 wherein said screen is flat and circular,wherein said partition means extends diametrically of said screen toform two compartments, and wherein said cover plate is semicircular sothat the edge thereof can be located, upon rotation of said cover plate,to cover the screen surface opposite either compartment and leave therest of the screen surface exposed to the eellulosic material.

3. Apparatus as in claim 1 including valve means connected to saidseparate conduits, means connected to said valve means for supplyingcleaning liquid under pressure, each valve means also connected to amain discharge conduit, said valve means operative such that with onevalve in position to connect its associated compartment conduit withsaid cleaning liquid the other valves are positioned to connect theirassociated compartment conduits with said main discharge conduitv 4.Apparatus as in claim 1 including a supply tank of cleaning liquid,means for supplying said cleaning liquid under pressure from said supplytank to one of said separate conduits when the compartment associatedwith that separate conduit is covered by said cover plate wherebycleaning liquid flows through said one conduit into said compartment,then through said screen into said cavity and then through said cleaningliquid discharge conduit.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 35 95 Dated June29, -97

Johan C.F.C. RICHTER Patent No.

Inventor(s) in the above-identified patent It is certified that errorappears corrected as shown below:

and that said Letters Patent are hereby In the front page format, line33:

"France" should read Sweden Signed and sealed this 7th day of March1972.

EDWARD PLFLb'TCIflRJR.

Commissioner of Patents Abtesting Officer USCOMM'DC 60376-P69 FORMPO-OSO (\0-69} n u s covzmmzm vnmnuc OFFICE uses o-zss-su

1. Apparatus for cleaning of screens inserted in containers fortreatment of finely comminuted cellulosic material and serving fordrawing off liquid from the cellulosic material, said apparatuscomprising: a cover plate covering a portion of the screen; means formoving the cover plate over the screen on the cellulosic material sidethereof, said cover plate having an edge closely applied against thescreen and surrounding a part of its surface and defining a cavity withsaid surface; a cleaning liquid discharge conduit extending through thecover plate and opening out into said cavity; means defining a chamberlocated on the opposite side of the screen from the cover plate;partition means dividing said chamber into separate compartments, saidpartition means having edges adjacent said screen opposite said coverplate which cooperate with the edge of said cover plate to maintain saidcavity in communicatIon with a given compartment, and a separate conduitconnected to each compartment for delivery thereto a stream of cleaningliquid when said cavity is in communication with said given compartmentwhereby cleaning liquid will flow through said screen from said givencompartment to said cavity and out through said discharge conduit. 2.Apparatus as in claim 1 wherein said screen is flat and circular,wherein said partition means extends diametrically of said screen toform two compartments, and wherein said cover plate is semicircular sothat the edge thereof can be located, upon 180* rotation of said coverplate, to cover the screen surface opposite either compartment and leavethe rest of the screen surface exposed to the cellulosic material. 3.Apparatus as in claim 1 including valve means connected to said separateconduits, means connected to said valve means for supplying cleaningliquid under pressure, each valve means also connected to a maindischarge conduit, said valve means operative such that with one valvein position to connect its associated compartment conduit with saidcleaning liquid the other valves are positioned to connect theirassociated compartment conduits with said main discharge conduit. 4.Apparatus as in claim 1 including a supply tank of cleaning liquid,means for supplying said cleaning liquid under pressure from said supplytank to one of said separate conduits when the compartment associatedwith that separate conduit is covered by said cover plate wherebycleaning liquid flows through said one conduit into said compartment,then through said screen into said cavity and then through said cleaningliquid discharge conduit.